1. Field of the Invention
The present invention relates to a base transceiver station (BTS) in a code division multiple access (CDMA) system and more particularly to a method of adjusting a size of a BTS search window for adjusting a size of a search window, which a BTS uses to acquire a signal of a mobile station, according to a service radius of the BTS in digital mobile communications.
2. Description of Related Art
A conventional CDMA system is illustrated in FIG. 1. The CDMA system usually comprises: a mobile station (MS) 10 which is operable while a user is moving or staying at any site; a base transceiver station (BTS) for receiving a call process request from the MS 10 and transmitting a call transmission request from a base station controller (BSC) 30 to the MS 10; the BSC 30 for controlling signal process between the BTS 20 and a mobile switching center (MSC) 40; the MSC 40 for transmitting the call process request from the MS 10 via a public network or a private network to a public switching telephone network (PSTN) or an advanced mobile phone service (AMPS) and other communication networks under control of the BSC 30, effecting a personal communication system (PCS) service; a home location register/visitor location register (HLR/VLR) 50 coupled to the MSC 40 for storing location information of the MS 10 subscribed to the MSC 40 and location information of the MS 10 within a service radius of the MSC 40; a base station manager (BSM) 60 coupled to the BSC 30 and having BTS search window size parameter information, for managing the BSC 30; and a voice mail system/fax mail system (VMS/FMS) 70 coupled to the MSC 40 for switching voice information transmitted in the form of voice and fax information to perform a voice/fax information service.
In the CDMA system having such configuration, when a subscriber having the MS 10 and being within the service area of the MSC uses the PCS service, the MSC 40 recognizes a location of the MS 10 via the HLR/VLR 50 and, in turn, performs the voice/fax information service in response to a request of the MS 10 or connects the MS 10 to another network, thereby effecting the PCS service. The BSM 60, which is coupled to the BSC 30 and has the search window size parameter information for the BTS 20, loads the parameter information onto the BTS 20 at an initial stage to allow to establish the size of the search window.
In this CDMA system, the BTS 20 establishes a range of time for searching, namely a search window, used for acquiring signals forwarded by the MS 10 and finds an access preamble of the MS 10. FIG. 2 shows a structure of an access channel. An access probe comprises an access preamble and a message. The access preamble consists of serial 94 zeros and is used to aid the BTS 20 in acquiring the MS 10. The message contains information necessary for the access.
Since the access preamble of the MS 10 consists of 94 zeros, the BTS 20 finds the access preamble by checking the number of input zeros in such a manner that a searcher of the BTS 20 correlates input signals with a walsh symbol index 0.
According to conventional technology, the search window for acquisition of the signals from the MS 10 is set to a certain value (for example, 1280) regardless of the service radius of the BTS 20.
Since the BTS uses the search window having the same size at the same position regardless of the service radius of the BTS 20 when acquiring an access signal of the MS in the conventional system, the BTS 20 having a smaller service radius may search an unnecessary range when finding the MS 10, so it takes much time for the BTS 20 to acquire the access signal of the MS 10, thereby frequently failing in acquiring the access signal of the MS 10. Additionally, the BTS 20 having a large service radius may not provide the service for the MS 10 located near the boundary of its service area, thereby deteriorating the quality of the mobile communication service.